Manufacture of metal having high emissivity



June 9, 1931. Q G, PINK 1,808,889

MANUFACTURE oF METAL HAVING HIGH EMIssIvITY Filed June 21, 1924 MIX/NGWl TH imam /40 TREA rllvq /N /g sara/Mu wmv AML/NE var/ons INVENTOR BY vATTORNEY Patented June 9, 1931 COLIN G. FINE, 0F YONKERS, NEW' YORKMANUFACTURE OF METAL HAVING HIGH EMISSIVITY Application led June 21,

This invention relates to a process for the manufacture of a metal oralloy having relatively high electronic emissivity and more particularlyto the manufacture of a metal adapted to be drawn into rods or filamentsfor use in electron discharge tubes and the like.

This invention has for its object generally to provide an improved andexpeditious procedure for producing a metal or alloy adapted to beeasily drawn into rods and filaments which have relatively highelectronic emissivity.

Specifically an object of this invention is to provide an improvedmethod of combining a metallic agent, adapted to provide a metallicframe or body having good working characteristics, with a second agentadapted to impart relatively high electronic emissivity to the resultingalloy or compound. l

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the several Asteps and the relationand order of one or more of such steps with respect to each of theothers thereof, which will be exempliiied in the rocess hereinafterdisclosed, and the scope ofJ the application of which will be indicatedin the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompan 'ng drawing, in which:

The gure shows schematically the character of the agents employed inthis process, the mode of combining, and the relative order of the,steps to be followedin practicin this invention.

n the practice of .this invention an agent which is adapted to provide ametallic frame or body is comblnedwith a second agent adapted to impartan electron-emitting property far in excess of that normallycharacteristic of the pure metals.

The agent supplying the metallic frame is for convenience hereinafterreferred to simply as the metallic agent. This agent 1924. serial No.721,493.

is to be very intimately mixed with the second agent which imparts thedesired electron-emissivity to the resulting alloy or compound. The formin which the metallic agent is' preferably added is therefore one inwhich the subdivision of the mass can be carried to a very high order.Salts and oxides of the metallic agent are forms adapted for thispurpose, the subdivision attainable being greater than for the puremetallic form. A soluble salt, however, is the more preferable, since bydissolving the agent, it may thus be subdivided into particles ofsubstantially molecular dimensions. The metallic body of the alloyshould be one capable of being heated to relatively high temperatureswithout fusing, should have relatively high electric resistance, andshould also be relatively resistant to oxidation at high temperatures.The metallic agent of this invention, by preference comprises the highlyrefractory metals such as molybdenum', tantalum, tungsten and the like.Where molybdenum is to be the metallic frame employed, the formof theagent supplying this metal is preferably a soluble 'salt for example,ammonium molybdate (NH4)2MoO4. The oxides -of molybdenum may however beused.

Thev second agent that imparts the electron emitting properties will behereinafter referred to as the emissive agent, and may be in the lformof a metallic compoun This second agent, however, should have as itsbase an element belongin to a chem- 85 ical group known to have highelectron emitting properties, particularly in comparison with therefractory metal providing the body of the alloy or compound hereproduced.

In the metallurgy of the refractory metals difficulty has beenexperienced in thoroughly reducing the metals. As a consequence it isdesirable that there' should be alloyed or'otherwise intimately mixedwith 95 the metallic agent a substance which is readily susceptible tooxidation. The emissive agent according to this invention should becomposed either wholly or in part of a metal that has the property ofbeing highly sus# lic agent of oxygen, the presence of oxides .havingbeen ascertained to be detrimental to the working and drawing propertiesof the alloy or compound produced.

The chemical group which is adapted to provide the second or emissiveagent includes the rare earths and the radio active elements, forexample, thorium, uranium, zirconium, and cerium. This agent ispreferably added to the first in the form of a soluble salt or compound,forfexample, in the form of a chlorate, chloride or nitrate. Wherethorium is the second agent used, thorium nitrate Th(NO3) 4, is asuitable salt for this purpose.

I have ascertained as set forth in my co pending application Serial No.686,628, filed Jan. 16, 1924, inthe metallurgy of the refractory metals,that it is desirable to combine with such a relatively volatile agentwhich is yadapted to be boiled out as it were from the metallicbody'during reduction thereby greatly facilitating the action of thehydrogen or reducing atmosphere in removing traces of oxygen from themetallic mass and otherwise freeing it ofintercrystalline impurities.

In the practice of this invention, there is accordingly added to themixture of the above two agents a third or volatile agent which enablesthe reducing process to remove effectively the oxygen andintercrystalline impurities to a degree which results in a highlyworkable alloy or compound which may be readily drawn into rods andfilaments adapted for copious electron emission in electron dischargetubes and the like. One or more volatile ingredients are added as thevolatile agent in such quantities as substantially to insure theirevaporization and complete boilin out from the metal under treatmentduring the step of reduction. The volatile agent includes preferablysalts of metals having relatively low boiling points as compared withthe melting temperatures of the metallic and emissive agents employed.Among suitable salts for this purpose are the volatile metallicchlorides, for example, cupric chloride, cuprous chloride, stanicchloride, stannous chloride, sodium chloride and cadmium chloride.

The agents of this invention are brought togetherl and mixed in suchproportions that the emissive agent will substantially alloy with themetallic agent and form, as it were, a solid solution containin theemissive agent. This bringing toget er is symbolically indicated in thedrawing. Where soluble salts are employed, the mixing as indicated iswith advantage effected by the aid of a water solution.

The step of mixing is followed by the step of drying in order properlyto condition the mixture for reduction. Where water solutions are to beprepared for reduction, this drying is preferably carried on in twostages. In the first stage the mixture is evaporated substantially todryness. In the second stage the mixture is baked to remove the lasttraces of water of crystallization, the dry mass resulting being thenpreferably broken into pieces preparatory to reduction.

The step of reduction follows the step of drying, and -is preferablyaccomplished in a dry hydrogen atmosphere by the aid of an electricfurnace. This step of reduction occupies several hours and is alsopreferably accomplished in two stages, namely, a preliminary stage inwhich the dry masses are brought to a temperature of 1200 C., and afinal stage in. which the temperature is brought to a degree approachingthe melting point. This latter stage of course occupies the greaterportion of time allowed for this step. Between these two stages thefused parts are preferably pressed together tightly so that when finallyheated in the electric mogeneous mass.

Following reduction is the step of drawin in which the reduced mass ismade into suitable slugs, rods or filaments as the case msg' be.

uch rods and laments are preferably given a final treatment in order toremove the last trace of surface oxides or other impurities which mayhave developed during the drawing operation. Such step is indicated inthe drawing as following the step of drawing, although the practice ofthis step is by no means essential to the practice` of this invention.This treatment is accomplished by the aid of a dry hydrogen atmospherepreferably saturated with the vapors of volatile hydrocarbon, forexample, aniline, pyridine, etc., the rod or filament being broughtsubstantially to incandescence during treatment by the aid of anelectric current. Such current is made to pass for a periodapproximating thirty seconds.

The following is an example of the procedure followed in practising theprocess of this invention: v

1,000 grams of ammonium molybdate are mixed by the aid of a watersolution with 7 5 grams of thorium nitrate; in this mixture is dissolved10 grams of sodium chloride and from 10 to 15 grams of cadium chloride.

The drying of this mixture is here accomplished in'two stages, it beingfirst evaporated to dryness and then baked and broken into suitablepieces.

furnace they become a sintered ho- The reduction is accomplished at highheat, by means of an electric furnace in a dry hydrogen atmosphere,preferably in two stages as above indicated.

The reduced mass from the electric furnace is then worked and drawnthrough dies` into ingots or slugs which mav be subsequently drawn intowires, rods and filaments.

These wires and filaments -are finally treated in an atmosphere of dryhydrogen,

more or less saturated with vapors of aniline; the finished wire beingheated to incandescence for a brief period with an electric current.

The drawn wire manufactured by this process is readily workableandretalns its pliability for a relatively long time. The product is toughand quite resistant to shock, and is substantially an alloy ofmolybdenum and thorium, the thoriated molybdenum thus producedpossessing an electron-emissivity many times greater than puredrawnmolybdenum. The phenomenon of electron-emissivity is very marked whenthe thoriated molybdenum is at relatively low temperature, for example,'that of a'dull red heat.

The electron-emissivity of the alloys of this invention is many thousandtimes greatei than that of pure refractory metals and mav be of theorder of magnitude gf 100,00'0

- times greater.

Since certain changes may be made lin carrying out the above processwithout departing from the scope of the invention, it is intended thatall matter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

It is. alsoto be understood that the following claims are intended t ocover all of the generic and' specific features of the invention hereindescribed, and all statements of Athe scope of the invention which, as amatter of language, might 'be said to fall therebetween.

Having described my invention, what I claim as new and desire to secureby Letters Patent, is:

1. The process of producin tallic alloy having relatively emissivity,comprisin mixing `together with the aid of water solu le saltscontaining respectively a metallic` agent, an emissive igh electronicagent and a volatile agent, drying and re-.

a ductile me-..

lic agent and a volatile agent, evaporating the mixture to dryness,baking the dried mixture, and subsequently reduclng the mixture in anatmosphere of hydrogen, the final stage of reduction being at atemperature suiicient to assure alloying.

3. The process of producing a readily workable alloy having relativelyhigh electronic emissivity comprising forming a solution in water ofwater soluble salts containing a metallic agent, an emissive metallicagent and a volatile agent, evaporating the mixture to dryness, bakingthe dried mixture, reducing the mixture in an atmosphere of hydrogen,pressing, completely sintering, the sintering temperature being suchasto assure alloying of the components, and drawing the reduced mass.

4. The process of -producing a readily workable refractory metallicalloy adapted to have relatively high electronic emissivity, comprisingmixing in solution ammonium molybdate, thorium nitrate and volatilemetallic salts, evaporating the mixture to dryness and baking, reducingin an atmosphere of hydrogen, the final stage of reduction being at atemperature suiiicient to assure alduced mass into filaments and thelike.

5. The process of producing a readily workable refractory metal alloyadapted to have relatively high electronic emissivity, comprising mixingin solution ammonium molybdate, thorium nitrate, and a volatile metallicchloride, evaporating the mixture to dryness and baking, reducing in anatmosphere of hydrogen, the final sta e of reduction being at atemperature su cient to as'- sure alloyin ,working and drawing the re`duced mass into filaments and the like, and subsequently'treating thesame to induce av desired temper.

6. The process of producing a readily workable alloy having relativelyhigh electronic emissivity comprising forming a solution containing ametallic agent, an emis- `sive metallic vagent anda volatile agent,evaporating the mixture to dryness, baking the dried mixture, reducingin an atmosphere of hydrogen the baked mixture, pressing,

sintering, .the sintering temperature being such as to assure alloyingof the components, drawing the reduced mass, and then treating the drawnrods in a dry hydrogen atmosphere while passing therethrough an electriccurrent.

7. The process of producing a readily workable refractory metallic alloyadapted yto have relatively high electronic emissivity comprisingmixingtogetheran agent conlOying, and subsequently drawing the resistingof a salt soluble in water containing molybdenum, a soluble agentvcontaining thorium, a soluble volatile a ent and water suilicient toproduce a desire solution, drying and reducing the mixture in a. dryhydrogen atmosphere, the final stage of reduction being at a temperaturesuiment to cause alloyng, and subsequently working and 5 drawing thereduced mass.

ture.

COLIN G. FINK.

In testimony whereof I aIix my signa.-

